MOOD OF FRUSTRATION, IMPOTENCE OUT OF SYNC WITH THIS PRESIDENCY

When President Reagan referred to "the so-called hostages" in Beirut in his press conference Tuesday night, you could tell he was worried about the parallels the reporters were drawing to the Iranian hostage crisis.

He had good reason for concern. The takeover of the U.S. Embassy in Tehran severely undermined the credibility of his predecessor, Jimmy Carter, and helped make him vulnerable to Reagan's challenge in 1980. For personal as well as humanitarian reasons, Reagan did not want anyone to think this was another "America held hostage" in the making.

His handling of the challenge has been designed to draw a sharp contrast between his way and Carter's way. Where Carter canceled all his previous engagements and threw himself into crisis management, Reagan has maintained most of his original schedule -- including the press conference.

Where Carter sought to focus world and domestic opinion sharply on the events in Iran, Reagan has sought to deny the terrorists the self-aggrandizing sense that they have moved every other issue and every other concern offstage. The unspoken purpose of the press conference and his other public appearances has been to communicate not that it is business as usual, with those American lives at stake, but that terrorism does not control the agenda of American life.

The final chapter of this tragic drama will determine how successful that effort will be. Reagan exhibited extraordinary self-control in the news conference, but it was still striking and painful to watch him acknowledge -- perhaps for the first time in his presidency -- that he was up against forces beyond his control.

Much of Reagan's aura and much of his appeal rest on the convincing picture he has conveyed of brimming self-confidence in himself and this nation. When Carter asked, in his autobiography and in his campaign, "Why not the best?," there was always a question mark in his tone of voice. When Reagan challenged America to "go for the gold" and promised the voters that "you ain't seen nothin' yet," he punctuated with oral exclamation points.

No problem, he said repeatedly, no problem is too big for free Americans to overcome, so long as we have faith in ourselves.

That was not the message, however, that Reagan delivered to a sober and listening nation on Tuesday. His answers were studded with references to "the impossibility" of the situation and the "frustration" Reagan shared with the watching millions.

In a previous time of anguish and frustration, after the 1983 suicide bombing of the Marine barracks in Beirut, Reagan sent American forces onto the island of Grenada and scored a quick victory. I offer no guess as to how he will respond this time, but it would very much surprise me if a political leader as sensitive to public moods as Reagan allowed this atmosphere of bewilderment, frustration and impotence to continue indefinitely.

Not only is his own reputation as an effective, optimistic president at stake, so are many of his cherished policy goals. That may seem exaggerated, but let me offer one example. I think the American voters' judgment of the strength of the nation's armed forces depends directly on how safe American citizens are in the world.

Reagan has asserted that his expensive defense buildup has made the United States more secure and more respected. Few voters can gauge the stockpiles of Soviet and U.S. missiles, but they draw clear inferences when terrorist tactics in small countries checkmate the clear national interest in individuals' freedom to move safely around the world.

This may be an inadequate yardstick, but it is an understandable one, and no amount of rhetoric will disguise the message of weakness that is conveyed by successful acts of terrorism against Americans abroad.

On Tuesday night the best of the limited options Reagans could discuss was a request to the secretary of transportation to caution Americans against flying into Athens, where the ill-fated TWA flight originated.

If that is his final response -- which I doubt -- this is going to be a different presidency in the next 3 1/2 years from the one we have seen until now.